Proper coating of many articles of manufacture is important to provide a desired function, give a pleasing aesthetic appearance, or to achieve protection against wear or the environment. Thermosetting plastic powder compositions are among many different coating materials that have been used on articles for these purposes as disclosed, for example, by a U.K. Patent Application GB2042930A (published Oct. 1, 1980) and a U.S. Pat. 3,953,644 (Camelon et al). These powder coatings are typically sprayed or otherwise applied to the article substrate and then heated to cure the powder into a hardened surface finish. However, it is difficult to obtain smooth finish coatings on plastics, plastic composites and fiber-reinforced plastic substrates which are porous and/or contain entrapped air and/or other volatile materials. This is due to a problem, known as "popping", which is believed to occur by release of volatile materials which erupt through the coating during heat curing of the coating.
Patents and other documents mentioned herein are incorporated by reference as if reproduced in full below.
Another problem in coating plastics and fiber reinforced plastic substrates is the need to substantially reduce hazardous Volatile Organic Compounds (VOCs), especially since the recent passage in 1990 of amendments to the Federal Clean Air Act (P.L. 101-549) which require such reductions. This need is particularly important where the application of a powder coating composition to a substrate is by electrostatic spraying, which also involves first applying a conductive paint to non-conductive substrates prior to coating with a powder composition. A solvent-based conductive paint typically has been used for this purpose, especially where the substrate is a wood fiber-reinforced plastic such as a phenolic cellulosic composite. However, a solvent-based conductive product has high emission levels of VOCs, such as xylene. The Clear Air Act Amendments of 1990 include xylenes (i.e., o-xylenes, m-xylenes and p-xylenes) on the list of hazardous air pollutants (HAPs) from stationary industrial sources whose emissions are or will be reduced by federal regulations.
Thus, it is and will be necessary to coat plastics and fiber reinforced plastic substrates using methods which will yield lower VOC (particularly xylene) emissions than the methods involving solvent-based conductive paints and/or conventional solvent based top coatings.